Whether there is life on Titan, the largest moon of Saturn, is at present an open question and a topic of scientific assessment and research. Titan is far colder than Earth, and its surface lacks stable liquid water, factors which have led some scientists to consider life there unlikely. On the other hand, its thick atmosphere is chemically active and rich in carbon compounds. On the surface there are bodies of liquid methane and ethane, and it is likely that there is a layer of liquid water under its ice shell; some scientists speculate that these liquid mixes may provide pre-biotic chemistry for living cells different from those on Earth.

In June 2010, scientists analysing data from the Cassini–Huygens mission reported anomalies in the atmosphere near the surface which could be consistent with the presence of methane-producing organisms, but may alternatively be due to non-living chemical or meteorological processes. The Cassini–Huygens mission was not equipped to look directly for micro-organisms or to provide a thorough inventory of complex organic compounds.

Superflares are very strong explosions observed on stars with energies up to ten thousand times that of typical solar flares. The stars in this class satisfy conditions which should make them solar analogues, and would be expected to be stable over very long time scales. The original nine candidates were detected by a variety of methods. No systematic study was possible until the launch of the Kepler satellite, which monitored a very large number of solar-type stars with very high accuracy for an extended period. This showed that a small proportion of stars had violent outbursts, up to 10,000 times as powerful as the strongest flares known on the Sun. In many cases there were multiple events on the same star. Younger stars were more likely to flare than old ones, but strong events were seen on stars as old as the Sun.

Oumuamua is the first known interstellar object to pass through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory, Hawaii, on 19 October 2017, 40 days after it passed its closest point to the Sun. When first seen, it was about 33,000,000 km from Earth (about 85 times as far away as the Moon), and already heading away from the Sun.

The Andromeda Galaxy (/ænˈdrɒmᵻdə/), also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda.

Being approximately 220,000 light years across, it is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 44 other smaller galaxies. Despite earlier findings that suggested that the Milky Way contains more dark matter and could be the largest in the grouping, the 2006 observations by the Spitzer Space Telescope revealed that Andromeda contains one trillion (1012) stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion.

Planet Nine is a hypothetical large planet in the far outer Solar System, the gravitational affects of which would explain the unusual orbital configuration of a group of trans-Neptunian objects (TNOs) that orbit mostly beyond the Kuiper belt.

The hypothesis first took form in a 2014 letter to the journal Nature by astronomers Chad Trujillo and Scott S. Sheppard, who had inferred the possible existence of a massive planet from similarities in the orbits of the distant trans-Neptunian objects Sedna and 2012 VP113. On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech argued that a massive outer planet would be the likeliest explanation for the similarities in orbits of six distant objects. The predicted planet would be a super-Earth, with an estimated mass of about 10 times that of Earth (approximately 5,000 times the mass of Pluto), a diameter two to four times that of Earth, and a highly elliptical orbit that is so far away that it could take around 15,000 years to orbit the Sun.

On the basis of models of planet formation that might include planetary migration from the inner Solar System, such as the fifth giant planet hypothesis, the authors suggest that it may be a primordial giant planet core that was ejected from its original orbit during the nebular epoch of the Solar System’s evolution.

An equinox is an astronomical event in which the plane of Earth’s equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September.

On an equinox, day and night are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the sun and atmospheric refraction. To avoid this ambiguity, the word equilux is sometimes used to mean a day in which the durations of light and darkness are equal. See Length of equinoctial day and night for further discussion.

Equinoxes on Earth

The equinoxes are the only times when the solar terminator (the “edge” between night and day) is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated.

In other words, the equinoxes are the only times when the subsolar point is on the equator, meaning that the Sun is exactly overhead at a point on the equatorial line. The subsolar point crosses the equator moving northward at the March equinox and southward at the September equinox.

The equinoxes, along with solstices, are directly related to the seasons of the year. In the northern hemisphere, the vernal equinox (March) conventionally marks the beginning of spring in most cultures and is considered the New Year in the Persian calendar or Iranian calendars as Nouroz (means new day), while the autumnal equinox (September) marks the beginning of autumn. In the southern hemisphere, the vernal equinox occurs in September and the autumnal equinox in March.